Enumeration of probiotic bacilli spores in animal feed: interlaboratory study.

Fourteen out of 17 laboratories completed an interlaboratory study comparing 2 pretreatment protocols of feed samples containing authorized probiotic bacilli spores. Both methods used tryptone soy agar for enumeration. Pretreatment A involved preparation of a suspension of the feed sample in 50% ethanol. For pretreatment B, the sample was suspended in peptone salt solution and heated at 80 degrees C for 10 min. Each laboratory analyzed 12 samples (6 per pretreatment), which represented duplicates of a high (10(9) colony-forming units [CFU]/g) and low (10(5) CFU/g) level of bacilli spores or a blank that contained vegetative probiotic bacteria only. For pretreatment A, the repeatability relative standard deviation (RSD(r)) was 2.9% for the low level and 2.5% for the high. The reproducibility relative standard deviation (RSDR) values were 7.8 and 5.9%, respectively. Pretreatment B revealed RSD(r) values of 1.1 and 1.0%, and RSDR values of 5.8 and 3.4%, respectively. The heat treatment (pretreatment B) of feed samples had better precision data, resulted in higher viable bacilli counts, and was more effective in deactivating vegetative background flora. It is therefore recommended for adoption for official control purposes and for CEN and ISO standards.

Distribution of Listeria spp. in confectioners' pastries from western France: comparison of enrichment methods.

Three hundred samples of pastry from 100 different suppliers in western France, including butter-cream, whipped dairy cream and custard filled cakes from each supplier, were collected and tested for the occurrence of Listeria spp. in 25 g samples. Listeria spp. were detected in 21.7% of he samples: Listeria monocytogenes in 13.7%, Listeria innocua in 10% and Listeria seeligeri in 2.3%. Thirteen samples were contaminated with two species simultaneously. The frequency of contaminated samples was not related to the composition of the pastry filling used, but it seemed to increase with the number of aerobic contaminant microorganisms in the dairy cream-based samples. The contamination rate was dependent on the place of manufacture. The numbers of Listeria spp. and Listeria monocytogenes were estimated on positive samples at the 25 g level as follows: < 0.3/g, Listeria spp. in 47 samples, L monocytogenes in 27; 0.3-30/g, Listeria spp. in 13, L. monocytogenes in nine; 30-300/g, L. monocytogenes in one; 300-3000/g; L. monocytogenes in three; 700,000/g, L. monocytogenes in one. Various detection methods were tested, including two enrichments broths tested in parallel: a modified LEB broth using 10 mg/l acriflavine-HCl and the UVM 1 broth, with incubation at 30 degrees C and streaking onto PALCAM agar. The enrichment procedures were: (a) primary enrichment of 25 g sample and plating after 48 h and 7 days; (b) secondary enrichment by subculturing the primary enrichment broths incubated for 24 h and 6 days, into fresh enrichment broth, then plating after 24 h incubation; (c) pre-enrichment of 25 g sample for 24 h in the basal enrichment broths without inhibitors, followed by subculturing in complete broths which were plated after 24 h and 6 days incubation. In all cases, UVM performed better than the LEB broth. It was unnecessary to extend the primary enrichment period beyond 48 h. Secondary enrichments inoculated from 24-h incubated primary enrichments gave a slightly better isolation rate than primary enrichments. Secondary enrichments made from 6-day incubated primary enrichments gave no additional advantage. The pre-enrichment procedure had an efficiency higher than that obtained by primary enrichment.